The present invention relates to a method for controlling a fuel pressure and more particularly to a method for holding a fuel pressure in high in a high pressure type direct fuel injection engine immediately after an engine stop.
Commonly, in a conventional high pressure type direct fuel injection engine ("high pressure type direct fuel injection engine" discussed herein is a fuel injection engine having a fuel injector for injecting fuel directly into a cylinder of an engine with a high pressure), the fuel pressure is released throughout the fuel system by letting a high pressure fuel regulator open upon an engine stop. This is in order to avoid problems caused in the fuel system, such as a fuel leakage from a fuel injector, deteriorations in relevant components and the like under a lasting high pressure being subjected to the fuel system.
However, when the fuel pressure is released at an engine stop, a vapor lock tends to occur in the fuel system due to a sudden pressure down of the heated fuel at portions where radiant heat is subjected from a heated engine and as a result, when an engine is tried to be restarted next after a short time, failed fuel injection is caused. Additionally, there occurs scuffing or sticking in bearing portions of a fuel pump due to insufficient lubrication.
To solve these problems, for example, Japanese patent application laid open No. 1985-116851 discloses a technology to eliminate a vapor lock at a restarting of engine in a hot condition by raising the fuel pressure in the fuel system so as to heighten a boiling point of fuel.
However, in an engine employing this prior art there is a problem of manipulation that a restarting of engine in a hot condition can not be made until the fuel pressure in the fuel system reaches a predetermined value. Hereinafter, "hot condition" of engine is referred to as a temperature condition under which vapor lock is caused in a fuel system of an engine.